skiffos/SkiffOS

Introduction

SkiffOS is a config package system for the Buildroot OS cross-compiler.

• Run any distribution anywhere: decouples hardware support from user distro environments.
• Reliable: minimal read-only host system for unbreakable boot-ups and over-the-air updates.
• Reproducible: offline builds, pinned package versions, source-controlled custom configs.

Configuration packages are merged together to configure the system:

• SKIFF_CONFIG=pi/4,core/debian - run Debian desktop on a Raspberry Pi 4.
• SKIFF_CONFIG=odroid/xu4,core/fedora - run Fedora desktop on a Odroid XU4.
• SKIFF_CONFIG=virt/qemu,custom/config - run a custom config in a Qemu VM.

There is a project template you can use for version-controlled customizations.

Linux devices have varying requirements for kernel, firmware, and other hardware support packages. SkiffOS decouples this support from the containerized environments. The containers are portable across devices with the same CPU architecture, while ordinary OS images (Board Support Packages) are not.

Supports any Linux-compatible computer, ranging from RPi, Odroid, NVIDIA Jetson, to Desktop PCs, Laptops (i.e. Apple MacBook), Phones, Cloud VMs, and even Web Browsers.

Supported Systems

The Buildroot OS cross-compiler can target any Linux-compatible device or virtual machine. These system configuration packages are available in the main SkiffOS repository:

All targets marked "tested" use automated end-to-end testing on real hardware. Targets marked "Obsolete" are discontinued by their manufacturer but still have a corresponding SkiffOS configuration and should still work.

Adding support for a board involves creating a Skiff configuration package for the board, as described above. If you have a device that is not yet supported by SkiffOS, please open an issue.

Getting started

Buildroot dependencies must be installed as a prerequisite.

This example uses pi/4 for the Raspberry Pi 4, see Supported Systems.

Create a SSH key on your development machine. Add the public key to your build with cp ~/.ssh/*.pub ./overrides/root_overlay/etc/skiff/authorized_keys. This will be needed to enable SSH access.

$ git submodule update             # make sure buildroot is up to date
$ make                             # lists all available options
$ export SKIFF_WORKSPACE=default   # optional: supports multiple SKIFF_CONFIG at once
$ export SKIFF_CONFIG=pi/4,skiff/core
$ make configure                   # configure the system
$ make compile                     # build the system

After you run make configure your SKIFF_CONFIG selection will be saved. The build can be interrupted and later resumed with make compile.

SKIFF_WORKSPACE defaults to default and is used to compile multiple SKIFF_CONFIG simultaneously.

There are many other utility commands made available by Buildroot, which can be listed using make br/help, some examples:

$ make br/menuconfig # explore Buildroot config menu
$ make br/sdk        # build relocatable SDK for target
$ make br/graph-size # graph the target packages sizes

There are other application packages available i.e. apps/podman and apps/crio.

Flashing the SD Card

Once the build is complete, it's time to flash the system to a SD card. You will need to switch to sudo bash for this on most systems.

$ sudo bash             # switch to root
$ blkid                 # look for your SD card's device file
$ export PI_SD=/dev/sdz # make sure this is right!
$ make cmd/pi/common/format  # tell skiff to format the device
$ make cmd/pi/common/install # tell skiff to install the os

The device needs to be formatted only one time, after which, the install command can be used to update the SkiffOS images without clearing the persistent data. The persist partition is not touched in this step, so anything you save there, including all Docker containers and system configuration, will not be modified.

Connecting

Connect using SSH to root@my-ip-address to access the SkiffOS system, and connect to core@my-ip-address to access the "Core" system container. See the section above about SSH public keys if you get a password prompt.

The mapping between users and containers can be edited in the /mnt/persist/skiff/core/config.yaml file.

OTA Upgrade

The system can then be upgraded over-the-air (OTA) using the rsync script:

$ ./scripts/push_image.bash root@my-ip-address

The SkiffOS upgrade (or downgrade) will take effect on next reboot.

Podman

Use the apps/podman configuration package to enable Podman support.

Running any distro in containers

SkiffOS Core runs Linux distributions in privileged containers:

• YAML configuration format for mapping containers, images, and users.
• systemd and/or other init processes operate as PID 1 inside the container.
• images can be pulled or compiled from scratch on first boot.

Adding skiff/core to SKIFF_CONFIG enables Debian Sid with an XFCE desktop.

Other distributions and images supported:

Other less frequently updated images:

There are also core images specific to pine64/phone and pine64/book and jetson/common.

Customize container config

The default configuration creates a user named "core" mapped into a container, but this can be adjusted with the skiff-core.yaml configuration file:

containers:
  core:
    image: skiffos/skiff-core-gentoo:latest
    [...]
users:
  core:
    container: core
    containerUser: core
    [...]

The provided example configs for the above supported distros are a good starting point for further customization.

To customize a running system, edit /mnt/persist/skiff/core/config.yaml and run systemctl restart skiff-core to apply. You may need to delete existing containers and restart skiff-core to re-create them after changing their config.

The configuration format and skiff-core source is in the skiff-core repo.

Configuration Packages

SkiffOS supports modular configuration packages: kernel & buildroot configs, root filesystem overlays, patches, hooks, and other resources.

Layers are named as namespace/name. For example, a Raspberry Pi 4 configuration would be pi/4 and Docker is apps/docker.

├── cflags:         compiler flags in files
├── buildroot:      buildroot configuration fragments
├── buildroot_ext:  buildroot extensions (extra packages)
├── buildroot_patches: extra Buildroot global patches
│   ├── <packagename>: patch files for Buildroot <packagename>
│   └── <packagename>/<version>: patches for package version
├── busybox:        busybox configuration fragments
├── extensions:     extra commands to add to the build system
│   └── Makefile
├── hooks:          scripts hooking pre/post build steps
│   ├── post.sh
│   └── pre.sh
├── kernel:         kernel configuration fragments
├── kernel_patches: kernel .patch files
├── root_overlay:   root overlay files
├── metadata:       metadata files
│   ├── commands
│   ├── dependencies
│   ├── description
│   └── unlisted
├── resources:     files used by the configuration package
├── scripts:       any scripts used by the extensions
├── uboot:         u-boot configuration fragments
├── uboot_patches: u-boot .patch files
└── users:         additional buildroot user config files

All files are optional.

Custom Users

To add custom users, add files in the "users" dir with the makeuser syntax.

Out-of-tree configuration packages

You can set the following env variables to control this process:

• SKIFF_CONFIG_PATH_ODROID_XU: Set the path for the ODROID_XU config package. You can set this to add new packages or override old ones.
• SKIFF_EXTRA_CONFIGS_PATH: Colon : separated list of paths to look for config packages.
• SKIFF_CONFIG: Name of skiff config to use, or comma separated list to overlay, with the later options taking precedence

These packages will be available in the SkiffOS system.

Overrides

It's often useful to be able to adjust the configs during development without actually creating a new configuration layer. This can be easily done with the overrides layer.

The overrides directory is treated as an additional configuration layer. The layout of the configuration layers is described above. Overrides is ignored by Git, and serves as a quick and easy way to modify the configuration.

To apply the changes & re-pack the build, run "make configure compile" again.

Workspaces

Use Workspaces to compile multiple SKIFF_CONFIG combinations simultaneously.

The SKIFF_WORKSPACE environment variable controls which workspace is selected.

The directory at workspaces/$SKIFF_WORKSPACE contains the Buildroot build directory.

Configuration files in overrides/workspaces/$SKIFF_WORKSPACE/ will override settings for that workspace using the configuration package structure.

Virtualization

The virt/ packages are designed for running Skiff in various virtualized environments.

Qemu

Here is a minimal working example of running Skiff in Qemu:

$ SKIFF_CONFIG=virt/qemu,util/rootlogin make configure compile
$ make cmd/virt/qemu/run

The util/rootlogin package is used here to enable logging in as "root" on the qemu debug console shown when running "cmd/virt/qemu/run".

Qemu can emulate other architectures, for example, riscv64:

export SKIFF_WORKSPACE=qemu
export SKIFF_CONFIG=virt/qemu,core/gentoo,util/rootlogin
mkdir -p ./overrides/workspaces/qemu/buildroot
echo "BR2_riscv=y" > ./overrides/workspaces/qemu/buildroot/arch
make compile

Most Buildroot-supported architectures can be selected & emulated.

The parameters for running the VM can also be adjusted:

export ROOTFS_MAX_SIZE=120G
export QEMU_MEMORY=8G
export QEMU_CPUS=8
make cmd/virt/qemu/run

Docker

Here is a minimal working example of running SkiffOS in Docker:

$ SKIFF_CONFIG=virt/docker,skiff/core make configure compile
$ make cmd/virt/docker/buildimage
$ make cmd/virt/docker/run

# inside container
$ su - core

The build command compiles the image, and run executes it.

You can execute a shell inside the container with:

$ make cmd/virt/docker/exec
# alternatively
$ docker exec -it skiff sh

Or run the latest demo release on Docker Hub:

docker run -t -d --name=skiff \
  --privileged \
  --cap-add=NET_ADMIN \
  --security-opt seccomp=unconfined \
  --stop-signal=SIGRTMIN+3 \
  -v /sys/fs/cgroup:/sys/fs/cgroup:ro \
  -v $(pwd)/skiff-persist:/mnt/persist \
  skiffos/skiffos:latest

Configuration

SkiffOS can also be configured with files in the "persist" partition.

Hostname

Set the hostname by placing the desired hostname in the skiff/hostname file on the persist partition. You could also set this in one of your config packages by writing the desired hostname to /etc/hostname.

NetworkManager

You can use nmcli on the device to manage NetworkManager, and any connection definitions written by nmcli device wifi connect or similar will automatically be written to the persist partition and persisted to future boots.

To connect to WiFi: nmcli device wifi connect myssid password mypassword.

The configuration file format for these connections is documented here with examples.

Example for a WiFi network called mywifi with password mypassword:

[connection]
id=mywifi
uuid=12f6c21d-f077-4b95-a4cb-bf41555d87a5
type=wifi

[wifi]
mode=infrastructure
ssid=mywifi

[wifi-security]
key-mgmt=wpa-psk
psk=mypassword

[ipv4]
method=auto

[ipv6]
addr-gen-mode=stable-privacy
method=auto

Network configuration files are plaintext files located at either of:

• /etc/NetworkManager/system-connections/ inside the build image
• /mnt/persist/skiff/connections/ on the persist partition.

To add the above example to your build:

• gedit ./overrides/root_overlay/etc/NetworkManager/system-connections/mywifi
• paste the above plaintext & save
• run "make compile" to update the image with the changes.

SSH Keys

The system will generate the authorized_keys file for the users on startup.

It takes SSH public key files (*.pub) from these locations:

• /etc/skiff/authorized_keys from inside the image
• skiff/keys from inside the persist partition

Your SSH public key will usually be located at ~/.ssh/id_ed25519.pub.

Mount a Disk to a Container

To mount a Linux disk, for example an ext4 partition, to a path inside a Docker container, you can use the Docker Volumes feature:

# create a volume for the storage drive
docker volume create --driver=local --opt device=/dev/disk/by-label/storage storage

# run a temporary container to view the contents
docker run --rm -it -v storage:/storage --workdir /storage alpine:edge sh

The volume can be mounted into a Skiff Core container by adding to the mounts list in /mnt/persist/skiff/core/config.yaml:

containers:
  core:
    image: skiffos/skiff-core-gentoo:latest
    mounts:
      - storage:/mnt/storage

After adding the mount, delete and re-create the container:

docker rm -f core
systemctl restart skiff-core

Whitepaper

The SkiffOS Whitepaper overviews the project motivation and goals.

Support

Community contributions are welcomed!

Please file a GitHub issue and/or Join Discord with any questions.

... or feel free to reach out on Matrix Chat!